In many deep ripping situations, it is desirable to leave the ground surface as undisturbed as possible to avoid the need for extensive surface preparation prior to other subsequent operations, such as seed planting. Many deep ripper points have a tendency, however, to cause surface eruptions on opposite sides of the tillage shank due to the lifting and fracturing action of wings and other inclined surfaces on the ripper point. Thus, it is known in the art to provide downwardly spring-biased ground wheels on opposite sides of the shank assembly to resist soil eruption at those locations and to press down and firm the ridges or berms created on opposite sides of the shank assembly. See for example U.S. Pat. Nos. 6,502,644 and 6,012,534.
However, in both of those prior patents, the two wheels associated with each shank assembly are pivotally mounted to the shank assembly on a common carrier that causes both wheels to rise and fall together as terrain changes are encountered by either one of the wheels. Because surface variations are often different on opposite sides of the shank assembly, rises encountered by one wheel will cause both wheels to lift even though the other wheel may not be experiencing the same condition. Consequently, the unnecessarily lifted wheel may fail to perform its downward pressing function in the most desired manner.
The present invention overcomes deficiencies in the prior art by providing a pair of firming wheels for each shank assembly that are separately and independently mounted to the shank assembly so that each wheel rises and falls independently of the other. Each wheel therefore reacts to soil conditions on its own side of the shank assembly without being affected by conditions encountered by the other wheel, to the end that a better overall firming action is obtained for the field.
Furthermore, in the present invention the down pressure wheels are mounted to the shank assembly in a simplified manner, i.e., by a spring for each wheel that serves the dual roles of a mounting means for the wheel and a source of down pressure or bias for the wheel. Preferably, the spring comprises a leaf spring. Instead of pivoting about a relatively short radius during up and down movement, each wheel simply moves up and down in a straight line path of travel as the leaf spring flexes during build up and release of its stored energy.
In one preferred embodiment, each leaf spring is generally J-shaped and is disposed in a horizontal attitude with its long leg extending fore-and-aft and the wheel attached to the rear end of the leg. The short leg of the spring is spaced below the long leg and is integrally attached thereto adjacent the front of the leaf spring by an arcuate bight portion of the spring. The short leg is attached to the shank assembly in a secure fashion so that primarily only the upper leg flexes as the wheel applies down pressure during field operations. The bight of the leaf spring is looped around an upright guide plate having an upper edge that forms a seat for the upper leg of the leaf spring and limits its downward flexing movement. Anti-twist structure comprising a pair of depending members on the leaf spring embrace the upright guide plate to prevent twisting of the upper leaf spring leg during the flexing action, while other interacting structure between the rear edge of the guide plate and the depending members keep the upper leaf spring leg moving in a rectilinear path of travel during its flexing motion. The short leaf spring leg is attached to the bottom edge of the guide plate, and provision is made to adjust the home position of each wheel by angularly adjusting the vertical position of the guide plate.